BMI linked with changes that may affect fertility

February 1, 2006

Montreal--Men with a body mass index indicative of being overweight or obese may exhibit changes in endocrine levels—notably lower testosterone levels—that could contribute to infertility, new research shows. It is possible, therefore, that fertility problems could be ameliorated with weight loss in some men.

"The typical American diet has over 2,000 calories, with less than three servings of the recommended six for fruits and vegetables," said lead investigator William E. Roudebush, PhD, a reproductive physiologist at Reproductive Biology Associates, Atlanta. "It's more high in fat, high in salt, less high in fiber, nutrients, and complex carbohydrates. People have stated that greater than 60% of Americans have a BMI greater than 25, which puts them in the obese category."

The poor lifestyle habits of Americans, leading to an ever-increasing BMI, may be having a significant effect on men's fertility levels.

"One question that was always asked is: What impact does that have on reproductive hormones?"

BMI and endocrine levels

Dr. Roudebush and his colleagues explored the relationship between BMI scores and serum reproductive endocrine levels in 90 male patients. They assessed serum reproductive levels using chemiluminescent assays. Testosterone levels were collected for all 90 patients, but other endocrine parameters were only collected in subsets of the men. Specifically, follicle-stimulating hormone (FSH) was collected in 12 men, luteinizing hormone (LH) in 36 men, and prolactin in 38.

For the analysis, patients were grouped according to their BMI. Those with a BMI of 20 to 24 were entered in a "normal" group. Those with a BMI of 25 to 30 went into the "overweight" group, and those with a BMI over 30 were placed in an "obese" group.

Regression analysis revealed a negative relationship between BMI and serum testosterone level. Mean serum testosterone levels were also significantly different among the three BMI groups, with the normal group having a mean level of 565 ng/dL, the overweight group having a mean level of 429 ng/dL, and the obese group having a mean level of 416 ng/dL. The differences in serum testosterone between normal versus overweight and obese men were both statistically significant, but the difference in testosterone levels between overweight and obese men was not.

"With decreased testosterone, these patients could present with decreased libido," Dr. Roudebush said. "There is the possibility for erectile dysfunction and impaired sperm production."

All other serum endocrine levels were similar among the three BMI groups, although there was a trend toward increased LH levels with higher BMI (p=.055). In addition, obese men had higher FSH levels than men of normal weight, and prolactin levels also tended to decrease with increasing BMI.

"We believe that with the addition of more data numbers, this will actually approach significance. We're in the process of collecting that data now," Dr. Roudebush said during his presentation.

"The bottom line is that BMI is going to impair sperm production, and we basically think that when men from infertile couples present at the clinic, if their BMI is greater than 25, their reproductive hormones should be evaluated," he told Urology Times.